I don't have the numbers handy, but if it reads zero empty, it can't be from a TR4. The TR4 sender reads zero full.
Flat glass is definitely TR4 or later; but early TR4 had curved glass gauges that look virtually identical (from the front) to TR3 gauges. However, if you look at the back of the gauge, the TR3 style gauge will have two slots & nuts on the outside for the adjustment (as shown below), while the TR4 gauge has two round windows (with slots possibly visible inside) and no nuts.